adding PatchContext - this will create new context with original + patch metadata

metadata/metadata.go

@@ -28,3 +28,17 @@ func FromContext(ctx context.Context) (Metadata, bool) {
 func NewContext(ctx context.Context, md Metadata) context.Context {
 	return context.WithValue(ctx, metaKey{}, md)
 }
+
+// PatchContext : will add/replace source metadata fields with given patch metadata fields
+func PatchContext(ctx context.Context, patchMd Metadata) context.Context {
+	md, _ := ctx.Value(metaKey{}).(Metadata)
+	cmd := make(Metadata)
+	for k, v := range md {
+		cmd[k] = v
+	}
+	for k, v := range patchMd {
+		cmd[k] = v
+	}
+	return context.WithValue(ctx, metaKey{}, cmd)
+
+}